In a constant velocity universal joint, which is used to construct a power transmission system for automobiles and various industrial machines, two shafts on a driving side and a driven side are coupled to each other to allow torque transmission therebetween, and rotational torque is transmitted at a constant velocity even when each of the two shafts forms an operating angle. The constant velocity universal joint is roughly classified into a fixed type constant velocity universal joint that allows only angular displacement, and a plunging type constant velocity universal joint that allows both the angular displacement and axial displacement. In a drive shaft for transmitting power from an engine of an automobile to a driving wheel, for example, the plunging type constant velocity universal joint is used on a differential side (inboard side), and the fixed type constant velocity universal joint is used on a driving wheel side (outboard side).
Irrespective of the plunging type and the fixed type, the constant velocity universal joint includes, as a main component, an outer joint member including a cup section having track grooves formed in an inner peripheral surface thereof to engage with torque transmitting elements, and a shaft section that extends from a bottom portion of the cup section in an axial direction. In many cases, the outer joint member is obtained by integrally forming the cup section and the shaft section by subjecting a rod-like solid material to a cold deformation process such as a forging process and an ironing process or a machining process such as a cutting process and a grinding process.
By the way, as the outer joint member, a shaft section that is long (long stem) may sometimes be used. In order to equalize lengths of a right part and a left part of the drive shaft, the long stem is used for an outer joint member on the inboard side that corresponds to one side of the drive shaft. The long stem is rotatably supported by a rolling bearing. Although varied depending on vehicle types, the length of the long stem section is substantially about 300 mm to 400 mm. In the outer joint member, the shaft section is long, which causes difficulty in integrally forming the cup section and the shaft section with high accuracy. Therefore, there is known an outer joint member in which a cup member forming the cup section and a shaft member forming the shaft section are constructed as separate members, and both the members are joined through friction press-contact. The joint member obtained by joining through the friction press-contact is disclosed in, for example, JP 2006-64060 A.
The outer joint member of the constant velocity universal joint illustrated in FIG. 5 of JP 2006-64060 A is described with reference to FIGS. 11 and 12. An intermediate product 51′ of an outer joint member 51 includes a component 52 serving as a cup member, a component 53 serving as a pipe member, and a component 54 serving as a stub member, and the components are joined through the friction press-contact. As illustrated in FIG. 11, burrs are generated at inner and outer diameters on joining portions 55 and 56 through the press-contact. In order to mount the rolling bearing (see FIG. 1) to a shaft section of the intermediate product 51′ of the outer joint member 51, it is necessary to remove burrs 55a and 56a on the outer diameter side of the joining portions 55 and 56 through a process such as lathing. Although not shown, the intermediate product 51′ is processed into a finished product of the outer joint member 51 through a machining process of a spline, stopper ring grooves, and the like. Therefore, the outer joint member 51 and the intermediate product 51′ have slight differences in shape, but illustration of the slight differences in shape is herein omitted to simplify the description, and the outer joint member 51 as the finished product and the intermediate product 51′ are denoted by the same reference symbols at the same parts. The same applies to the description below.